Switching assembly



Sept. 11, 1962 J. F. DUFFIELD SWITCHING ASSEMBLY Filed July 1, 1960PRIOR ART FIG.2

FIG.1

PRlOR ART JOSEPH FREDER/CKDUFF/ELD In ven tor Atforne y United StatesPatent 3,053,957 SWITCHING ASSEMBLY Joseph Frederick Dufiield,Agincourt, Ontario, Canada,

assignor to Amalgamated Electric Corporation, Limited, Toronto, Ontario,Canada Filed July 1, 1960, Ser. No. 40,331 1 Claim. (Cl. 200-466) Thisinvention relates to an electrical switching assembly of the typecomprising two spaced-apart, resilient contact plates adapted to receivea moveable contact member slidably therebetween in contact makingengagement therewith.

More particularly, in accordance with my invention, I provide, in aswitching assembly of the aforementioned type, a downwardly extendingflap in at least one of the contact plates, the flap being formed so asto provide a contact making surface with the moveable contact member.

Prior art switching assemblies include a pair of spacedapart, resilientcontact plates, which, when they receive a moveable contact membertherebetween, move slightly outwardly relative to one another, and byvirtue of their resilience grip the moveable contact member. In order toprovide the necessary resilience, the contact plates usually have lowerportions inclined towards one another so that the spacing between theupper part of the lower portions is less than the spacing between thelower part of the lower portions. Generally the upper portions of thecontact plates, i.e. the portions adjacent the upper part of the lowerportions, are oppositely inclined so as to facilitate insertion of themoveable contact member between the contact plates. As will be apparentat a later point, switching assemblies of this type substantially reducethe amount of surface contact between the contact plates and themoveable contact member, thereby tending to cause heating of the switchassembly, hence watts lost in the switch assembly and reducedefiiciency.

It is therefore an object of my invention to provide an electricalswitching assembly including means to permit increased surface contactbetween the contact plates and the moveable contact member.

It is another obejct of my invention to provide a new and improvedelectrical switching assembly which, by virtue of its construction,materially improves surface contact between the contact plates and themoveable contact member, thereby decreasing the heating of the switchassembly when current is passed therethrough and increasing the overallefficiency of the circuit in which the switch assembly is employed.

Other objects and advantages of the apparatus embodying my inventionwill become apparent from the following detailed description anddrawings in which:

FIGURE 1 shows in side elevation a pair of prior art spaced-apart,resilient contact plates;

FIGURE 2 shows in side elevation a prior art switching assemblyincluding a moveable contact member positioned between two spaced-apartresilient contact plates;

FIGURE 3 shows in perspective an electrical switching assemblyconstructed in accordance with one embodiment of my invention; and

FIGURE 4 is a side elevation in section of the embodiment of myinvention shown in FIGURE 3.

In brief, an electrical switching assembly constructed in accordancewith my invention comprises two spacedapart contact plates, at least oneof which is resilient, adapted to receive a moveable contact memberslidably therebetween in contact making engagement therewith. Adownwardly extending flap is formed in at least one of the contactplates, the flap 'being formed by slits in one of the contact plates andinwardly bent about an unslit side out of the plane of the contact plateand to- 3,053,957 Patented Sept. 11, 1962 wards the other of the contactplates. The flap thereby provides a contact making surface with themoveable contact member. It should be noted that the term contact makingsurface as used herein, is to be interpreted in the macroscopic ratherthan the microscopic sense, since, as is well known, unless two flatsurfaces are optically polished, there will not be true surface contactbetween them, rather the contact will be in the nature of numerousisolated point contacts.

In FIGURES 1 and 2 I have shown two spaced-apart, resilient contactplates generally designated 1 and 2 fastened together by suitable means(not shown) which prevent any movement of one plate relative to theother. Each contact plate has a lower portion 3 and an upper portion 4.The lower portions 3 are inclined towards one another so as to form adownwardly opening space therebetween so as to provide the necessaryresilience. The upper portions 4 are oppositely inclined so as to forman upwardly opening space therebetween, thereby facilitating insertionof a moveable contact member 5 (FIG- URE 2) therebetween.

When moveable contact member 5 is inserted between contact plates 1 and2, the plates spring apart slightly, and by virtue of their resilience,tend to grip moveable contact member 5 therebetween. In order to impartresilience to contact plates 1 and 2, the lower portions 3 thereof areinwardly inclined as shown and described. It will be apparent that ifcontact plates 1 and 2 were parallel to one another and the spacingtherebetween was the same as the width of moveable contact member 5,surface contact between contact plates 1 and 2 and moveable contactmember 5 would be poor because of the lack of resilience in contactplates 1 and 2 and the consequent low pressure between the plates andmoveable contact member 5, thereby resulting in undesirable heating ofthe switch assembly and reduced circuit efficiency. Hence, prior artassemblies have generally followed the form of construction outline inFIGURES 1 and 2.

It will be apparent from a consideration of FIGURE 2, however, that goodsurface contact between contact plates 1 and 2 and moveable contactmember 5 is achieved only at the upper part of lower portions 3, andthat the pressure between contact plates 1 and 2 and moveable contactmember 5 steadily decreases towards the lower part of lower portions 3.Eventually a point is reached where there is no surface contact at all,and a relatively large area on the lower part of lower portions 3 ofplates 1,

and 2 is not in contact with movable contact member 5. Since the amountof mating surface area between two electrically contacting members andthe pressure with which they are held together determines the amount ofcurrent that can be passed between the members without undue heating, itwill be apparent from a consideration of FIGURE 2 that the switchassembly shown therein is not efficient inasmuch as it provides only asmall amount of surface contact with steadily reducing contact pressure.Hence for large currents passing between moveable contact member 5 andcontact plates 1 and 2, there will be a large amount of heating andresultant switch and circuit inefiiciency.

While in the prior art switching assembly just described, good surfacecontact between contact plates 1 and 2 and moveable contact member 5 isachieved only at the upper part of lower portions 3, if contact member 5is wider than the spacing between the lower part of lower portions 3,good surface contact between contact plates 1 and 2 and moveable contactmember 5 will be achieved only at the lower part of lower portions 3,the upper part of lower portions 3 and upper portions 4 being forcedaway from contact member 5. This also is undesirable for the samereasons as previously mentioned.

Referring now to FIGURES 3 and 4 wherein I have illustrated anelectrical switching assembly embodying my invention, I have shown apair of contact plates 1' and 2 made of an electrically conductingmaterial such as, for example, copper, each having lower portions 3' andupper portions 4. Lower portions 3' form a downwardly opening spacetherebetween, and upper portions 4 'form an upwardly opening spacetherebetween so as to facilitate insertion of a movable contact member 5therebetween. Preferably contact plate 1 is mounted so as to be parallelto contact member 5, contact plate 2' being slightly inclined withrespect thereto. Contact plates 1' and 2' could be inclined towards oneanother in the manner shown in FIGURES 1 and 2 with a possible slightreduction in total contact area from the preferred embodiment. While inthe embodiment of my invention illustrated in FIGURES 3 and 4 bothcontact plates 1 and 2 are resilient, it will be apparent that contactplate 1' could be non-resilient. For example, it could be made of arelatively massive block of copper. In accordance with my invention, aflap 6 is formed by slits in contact plate 2'. Flap 6 is inwardly bentabout an unslit side out of the plane defined by lower portion 3' ofcontact plate 2' and towards contact plate 1' to form a flap which ismore resilient than contact plate 2'. As best shown in FIGURE 4, flap 6provides a contact making surface with moveable contact member 5'. Sincecontact plate 1' is parallel to contact member 5', thereby establishinglarge area surface contact with one side of contact member 5' and flap 6makes a large area surface contact with the opposite side of contactmember 5' by virtue of its resilience and inwardly bent position, andthere is contact pressure between contact plate 1', contact member 5'and flap 6 it will be apparent from a comparison of FIGURES 2 and 4 thata switching assembly embodying my invention provides a greater contactmaking surface between moveable contact member 5' and contact plates 1'and 2 than is possible with the prior art switching assembly shown inFIGURE 2. As an additional feature of my invention, a strong, springclip 7, which may be made of spring steel, may be provided bridging thesides of contact plates 1' and 2 and urging flap 6 towards contact plate1'. In this manner the contact pressure between contact plate 1', flap 6and moveable contact member 5 may be substantially increased. Thus itwill be seen that I have provided a switching assembly having bothincreased pressure and increased surface area between the contact makingsurfaces thereof.

It should be noted that it is also possible to provide a flap 6 incontact plate 1' in which case it is preferable that lower portions 3'of contact plates 1' and 2' be inclined towards one another slightly, asin the case of contact plates 1 and 2 shown in FIGURES 1 and 2. Thegreater is the contact making surface area of flap 6, the greater willbe the rating of the switch i.e. the amount of current the switch cancarry without undue heating.

It will be apparent that moveable contact member 5 could be the knifeblade of a conventional knife blade switch, the terminal of aconventional fuse or any other electrically conducting moveable memberrequired to be inserted between a pair of contact plates and establishgood electrical contact therewith. It is, therefore, in this sense thatthe terminology switching assembly is to be interpreted.

It will be understood that while I have described and illustratedvarious embodiments of my invention, changes and modifications thereofmay be made without departing from the spirit and scope of the inventionas defined in the appended claims.

What I claim as my invention is:

In a switching assembly of the type comprising two spaced-apartgenerally L-shaped contact plates having portions thereof defining adownwardly opening space therebetween and adapted to receive a moveablecontact member slidably therebetween in contact making engagementtherewith, said portion of one of said contact plates being parallel toand in surface contact with a side of said contact member, said portionof the other of said contact plates being inclined inwardly and upwardlytoward said contact member, at least said other contact plate beingresilient, the improvement which comprises a downwardly extending flapin said portion of said other contact plate, said flap being formed byslits in said other contact plate and being inwardly bent into thedownwardly opening space about an unslit side out of the plane of saidportion of said other contact plate and towards said portion of said onecontact plate, at least substantially all of one surface of said flapproviding thereby a contact making surface with another side of saidcontact member, and a spring clip bridging said contact plates from thesides thereof and urging said flap toward said one contact plate.

References Cited in the file of this patent UNITED STATES PATENTS790,883 Buchanan May 30, 1905 2,085,707 Shore June 29, 1937 2,659,063Webb et al Nov. 10, 1953 2,889,533 Nielsen June 2, 1959 FOREIGN PATENTS634,400 Germany Aug. 27, 1936

